This invention relates generally to heating element assemblies used in heater and boiler tanks for heating and boiling liquids such as water and other aqueous solutions. More specifically, this invention relates to fully removable heating element assemblies used in heater and boiler tanks which also permit removing selected individual heating elements for inspection, cleaning and/or repair and which permit replacing of worn, damaged or defective ones of such elements, all with reduced effort and reduced heater or boiler down-time.
One important application of such assemblies is in boilers used in carbon dioxide (CO.sub.2) removal air purification systems. Such systems are employed in closed atmospheric environments to prevent the accumulation of high concentrations of CO.sub.2 caused by human and animal exhalation. Excessive CO.sub.2 build-up in a closed breathing environment can cause breathing difficulty, drowsiness and, in extreme cases, even death. A typical prior art CO.sub.2 removal system utilizes a relatively cool solution of water and monoethanolamine (MEA) to absorb excessive amounts of CO.sub.2 from a closed atmosphere. The CO.sub.2 enriched MEA solution is thereafter cycled through a boiler where it is heated to drive off the absorbed CO.sub.2, whereby gaseous carbon dioxide is separated from the closed atmosphere and collected for venting to external ambient atmosphere. The CO.sub.2 depleted (lean) MEA solution is thereafter condensed and cooled back to approximately room temperature and recycled to an absorber tower where it contacts the closed atmosphere to absorb more CO.sub.2.
One difficulty that has been encountered in the boilers of such prior art CO.sub.2 removal systems resides in the fact that the individual electrical heater elements of the boiler heating element assembly are in direct contact with the MEA solution being heated. Such direct contact tends to cause breakdown of the MEA over a period of time which lessens its efficiency in absorbing CO.sub.2 from the closed atmosphere. Moreover, as the MEA breaks down, it changes the aqueous solution from a clear to a black liquid which, in turn, causes increased corrosion of not only the heating elements but other fixtures within the system. Indeed, over a period of time solids will form in the MEA solution which tend to interfere with valve operation and liquid flow, cause corrosion in pipe fittings, plug strainer elements and produce gasket leaks. Another difficulty that has been noted using prior art heater element assemblies whose elements directly contact the solution being boiled is the tendency of such elements to short out. This is an especially dangerous situation where high voltages of as much as 440 volts are employed to heat the heater elements.
Another difficulty noted in the use of heater element assemblies in boilers which permit direct contact between the individual heater elements and the liquid being boiled is the inability to remove the same for inspection, cleaning, repair and/or replacement without first shutting down the system to allow the boiler to cool. Depending upon the size of the boiler and the mass of liquid involved, the resulting boiler down-time can be significant. In view of the possibility of dangerous arcing due to short circuits which can occur with worn, damaged or corroded heater elements, it would be highly desirable to be able to perform frequent inspections of the heater elements as part of a preventive maintenance program. However, such inspections of the prior art heater assemblies would involve excessive and often unacceptable periods of boiler down-time. Another problem resulting from the use of prior art heating element assemblies is the relevative difficulty and delay encountered when removal of the entire heating element assembly from a boiler becomes necessary.
By means of our invention these and other problems encountered in the use of prior art heating element assemblies in fluid heaters and boilers are substantially eliminated.